1. Field of the Invention
Embodiments of the invention generally relate to an apparatus and method for loading a substrate on a carrier head.
2. Description of the Related Art
Sub-micron multi-level metallization is one of the key technologies for the next generation of ultra large-scale integration (ULSI). The multilevel interconnects that lie at the heart of this technology require planarization of interconnect features formed in high aspect ratio apertures, including contacts, vias, trenches and other features. Reliable formation of these interconnect features is very important to the success of ULSI and to the continued effort to increase circuit density and quality on individual substrates and die.
Planarization is generally performed using Chemical Mechanical Polishing (CMP) and/or Electro-Chemical Mechanical Deposition (ECMP). A planarization method typically requires that a substrate be mounted in a carrier head, with the surface of the substrate to be polished exposed. The substrate supported by the carrier head is then placed against a rotating polishing pad. The head holding the substrate may also rotate, to provide additional motion between the substrate and the polishing pad surface.
During planarization, a substrate is typically mounted on a carrier head by way of a vacuum chuck. A carrier head typically has an flexible membrane providing a mounting surface configured to receive the substrate from a backside. The flexible membrane may have one or more chambers connecting to a fluid source. When the fluid, such as air, is pumping into the chambers, the volume of the chambers will increase and the flexible membrane will be forced downwardly. On the other hand, when the fluid is pumped out of the chambers, the volume of the chambers will decrease and the flexible membrane will be forced up. To load the substrate, the carrier head generally moves to a position where the flexible membrane is positioned approximate the back side of the substrate. The flexible membrane is lowered by pumping fluid into the chambers and the mounting surface is positioned against the back side of the substrate. Fluid may then be pumped out of the chambers so that the flexible membrane may bow inwardly creating a low pressure pocket between the mounting surface and the back side of the substrate. The low pressure pocket will vacuum chuck the substrate to the carrier head.
FIGS. 1A-B schematically illustrate a typical substrate loading process used in the state of the art systems. A base member 102 is generally adapted to a carrier head (not shown). A flexible membrane 105 providing a substrate mounting surface 106 is mounted on the base member 102. The flexible membrane 105 has a center chamber 103 and an edge chamber 104. The center chamber 103 is configured to push out or draw in the mounting surface 106. The edge chamber 104 is generally configured to form a seal near an edge of a substrate 101 during the loading process.
As shown in FIG. 1A, both of the center chamber 103 and the edge chamber 104 is inflated by flowing fluid so that the mounting surface 106 is pressed against a backside 107 of the substrate 101. As the edge chamber 104 increases in volume, a seal may be formed between the mounting surface 106 and the backside 107 near the edge. Shown in FIG. 1B, the center chamber 103 may be deflated by pumping out fluid after the seal has been formed. The deflation of the center chamber 103 causing the mounting surface 106 to move upward. Because of the seal at the edge of the mounting surface 106, a volume of low pressure or vacuum will form between the mounting surface 106 and the backside 107 as the mounting surface moving upward forcing the substrate 101 against the mounting surface 106. The substrate 101 is, therefore, sealingly loaded on the flexible membrane 105. Because the substrate 101 is pushed downward around the edge to form the seal, and pulled upward by the vacuum force near the center, the substrate 101 goes through bowing deformation which introduces stress to the substrate and sometimes even breaks the substrate. A relatively large amount of fluid, such as control gas, must be moved to inflate the chambers and to pull vacuum from the inflated chambers.
Thus, the typical substrate loading process described above has at least two disadvantages. In one aspect, the loaded substrate usually goes through high bowing deformation causing occasional substrate breakage. In another aspect, inflating and deflating the flexible membrane requires moving relatively large volume of fluid which takes additional time.
Therefore, there is a need for an apparatus and method to improve the substrate loading process.